This invention relates to engine fuel controls and more particularly to fuel controls having means for automatically sensing an engine operating abnormality and, in response thereto, positively shutting off fuel flow to the engine until favorable restarting conditions obtain.
It is known that during starting, or during operation after starting, of an engine such as a gas turbine engine, engine operating abnormalities may occur which require positive shutoff of fuel flow to the engine to prevent damage to the engine itself or to the unit driven thereby. During starting, for example, improper ignition runs the risk of creating a "hot start" wherein excessive fuel collects in the combustion section of the engine which, if ignited, may overheat and damage the engine. Similarly, during engine running, abnormal and potentially dangerous engine conditions may occur, such as overspeed of the gas generator or the free turbine, which require positive shutoff of all fuel flow to the engine.
In addition to rapid and effective initiation of fuel cutoff upon the occurrence of the engine abnormality, there is recognized the need for such cutoff to continue until favorable engine restarting conditions are attained. If fuel cutoff lasts only as long as the engine abnormality, the return of flow will likely be under conditions not conducive to restarting.